The present invention relates to the angular deviation measurement art and, more particularly, to an electronic protractor.
In many applications, the need exists for a lightweight, highly accurate protractor. An excellent example of this need is found in the commercial aircraft industry. There, the precise angle of horizontal control surfaces must be measured to insure proper response of the aircraft's hydraulic actuating systems to commands from the flight director computer.
The prior art technique for measuring aircraft control surface rotation involves affixing on the airplane a large, heavy aluminum protractor. This protractor clamps to the non-rotating aircraft surface, with the rotating surface carrying a cursor pointing to the graduations engraved on the protractor body.
This technique suffers from numerous problems. First, it is a two-person operation. One person rotates the controls from the cockpit and the other observes the cursor position at the protractor. Second, the cost of such protractors is high, due to both the nature and quantity of materials involved and the requisite labor. Further, installation is awkward since a crane must be used to install the protractor on the aircraft due to the high protractor weight. This results in the possibility of damage to the aircraft skin if the protractor is improperly lowered into place. In addition, the zero reference plane of the protractor is subject to move due to its great weight on the aircraft control surface.
Efforts have been made in the angle measuring art at developing electronic protractors. However, none of the available designs has proven suitable in applications such as described above in the aircraft industry. A principal problem with prior designs is that they are highly subject to error due to vibration. In addition, whereas such prior electronic protractors are capable of measuring relatively large angles with precision, deficiencies in their design have rendered them incapable of accurately resolving small deflections.